1. Field of the Invention
The present invention is related to a triaxial (3-axis) acceleration sensor and a method of manufacturing a triaxial (3-axis) acceleration sensor.
2. Description of the Prior Art
Conventionally, a triaxial (3-axis) acceleration sensor is known that can detect acceleration in 3-axis directions, for example. The 3-axis acceleration sensor known in the art includes: a support frame of substantially rectangular shape made of silicon; a plurality of thin beams with flexibility provided inside the support frame; a weight member oscillatably supported by the plurality of beams; and a plurality of bridge circuits constituted from piezo resistance elements respectively disposed on the beams and interconnected by metallic wiring lines.
Such a triaxial acceleration sensor generally has a configuration in which, in order to prevent excessive displacement of a weight member within a housing, a gap is formed in the housing so as to surround the weight member so that the weight member is supported in a freely suspended state. In the case where a triaxial acceleration sensor module is constructed from such a triaxial acceleration sensor, a sensor driving IC for driving the triaxial acceleration sensor, various elements such as resistance elements and capacitors, and the like are integrally formed on a module substrate (or in a package) in addition to the triaxial acceleration sensor (see Japanese Patent Laid-open Publication 2000-105252 as an example of a packaged semiconductor acceleration sensor).
Although such a conventional triaxial acceleration sensor module can be made thinner by arranging its components such as a triaxial acceleration sensor module on a module substrate in a planar manner, the setting area of the conventional triaxial acceleration sensor module becomes larger for that. For this reason, it is difficult to make the whole module smaller. On the other hand, in the case where a triaxial acceleration sensor and a sensor driving IC and the like are arranged on both major surfaces of a module substrate so as to be stacked with each other, it is difficult to make the whole module thinner though it is possible to make the setting area thereof smaller.
Further, as described above, the conventional triaxial acceleration sensor is provided with a gap so as to surround the weight member for assuring sufficient displacement of the weight member and preventing damage due to the excessive displacement of the weight member. This obstructs making the triaxial acceleration sensor module itself thinner.